This invention relates to dynamoelectric machines and, in particular, to dynamoelectric machines of the type including a rotor having electrically conductive windings disposed in a plurality of axially extending slots.
A dynamoelectric machine includes a rotor body having a plurality of axially extending slots into which electrical windings are inserted. The rotor body is generally a steel material whereas the rotor windings comprise a plurality of copper wires. In a direct-cooled dynamoelectric machine each slot may further include an axially extending sub-slot for ventilation and cooling. The direct-cooled machine is one which is cooled directly by the atmosphere in which it is disposed, e.g., air or hydrogen. The sub-slots are part of a ventilation scheme, known in the art, for transferring gas coolant axially along the rotor. Each slot also includes provision for the radial flow of gas coolant, primarily through ventilation slots in the windings.
In the aforementioned machine it is necessary to electrically insulate the rotor windings from the rotor body, such insulation taking the form of nonconductive "slot-armor". One such insulation is shown in U.S. Pat. No. 4,321,498 to Vogt and assigned to the assignee of the present invention. In that patent, herein incorporated by reference, it is suggested that a preferred embodiment of the invention would include a pair of electrical insulating members (slot armor), each member comprising a radially extending portion terminating in a base leg, the electrically insulating members disposed in each slot so that the radially extending portions are adjacent opposite slot walls and the base legs extend towards one another. In addition, there is an axially extending base (sub-slot cover) having opposite sides formed with axially extending grooves for accepting therein each opposite base leg whereby an interlocking joint is formed between the sub-slot cover and the slot armor. It is further suggested that both the sub-slot cover and the insulating slot armor disposed adjacent the slot walls would be formed from glass laminate material.
The applicants have found it desirable to use an aramid paper such as Nomex (trademark, DuPont Company) as an insulating material for the slot armor. However, in following the teaching of the previous U.S. Pat. No. 4,321,498 they have found that there is a lack of rigidity which occurs in the 90 degree bend at the interlocking section of the insulating member and the base member. Under centrifugal load, the slot armor will migrate up the slot wall pulling away from the interlocking section of the sub-slot cover.
Aramid paper is presently used in conventionally-cooled machines only. Conventionally-cooled machines are described as other than direct-cooled machines. Conventionally cooled machines are machines wherein cooling of the windings occurs by transfer of heat from the windings through the body of the rotor and then into the cooling medium. In the direct-cooled machine, the cooling medium is passed directly through the windings. Aramid paper will exhibit dimensional instability and can increase axially in length as much as one percent under changing conditions of relative humidity. Therefore, even U-shaped aramid paper with punched ventilation slots has been avoided in direct-cooled windings because humidity can cause the registration of the ventilation slots for the sub-slot cover-slot armor and copper to become misaligned, thus reducing the area of cooling paths.
In U.S. patent application Ser. No. 656,571 filed Oct. 1, 1984, now U.S. Pat. No. 4,560,896 and assigned to the assignee of the present invention, there is disclosed one solution to the above stated problem involving aramid paper using a composite aramid paper slot armor and glass laminate sub-slot cover. The slot armor is comprised of axially and radially extending sidewalls joined together by a radially inner, axially extending base portion to form a "U"-shaped channel. The sub-slot cover comprises a planar outer layer (with respect to the rotor centerline) and a planar inner layer. The aramid paper is formed with spaced-apart holes which allow the inner and outer planar layers of the sub-slot cover to be bonded to one another as well as to the aramid paper base portion inserted therebetween. Ventilation slots are thereafter machined into the slot armor sub-slot composite.
Although the solution of the above cited application provides an improved system, it requires a bonding operation followed by a machining operation in order to form the composite structure.
Accordingly, it is an object of the present invention to provide an improved slot insulation for dynamoelectric machine which overcomes the deficiencies of the prior art.
It is another object of the present invention to provide an improved slot insulation for a dynamoelectric machine utilizing a two piece injection molded sub-slot cover in which the first and second piece may be mechanically fastened without the use of a bonding agent.
It is a still further object of the present invention to provide an improved slot insulation for a dynamoelectric machine utilizing a substantially U-shaped aramid paper insulation in combination with an injection molded sub-slot cover in which the sub-slot cover can be mechanically fastened to the insulation to form a composite structure without the use of a bonding agent.
It is still another object of the present invention to provide an improved sub-slot cover for a dynamoelectric machine which can be manufactured in a standard length and mechanically joined to form a continuous axial sub-slot cover.
It is still another object of the present invention to provide an improved sub-slot cover for a dynamoelectric machine wherein the sub-slot cover is formed of two pieces of injection molded insulation material having preformed ventilation holes for mating with ventilation holes in a slot insulation member.